1. Field of the Invention
The present invention relates to an open-barrel type crimp terminal having concave serrations in an inner surface of a conductor crimping portion having a U-letter shaped cross section.
2. Description of the Related Art
Conventionally, a general crimp terminal is, for example, provided with an electrical connection portion, a conductor crimping portion, and a sheath crimping portion as shown in Patent Literature 1 (Japanese Patent Application Laid-Open Publication No. 2010-198776). The electrical connection portion is provided at a front in a longitudinal direction of the terminal (in a same direction as a longitudinal direction of a conductor of an electrical wire connected to the terminal), and is connected to a terminal of a mating connector. The conductor crimping portion is provided closer to a rear than the electrical connection portion in the longitudinal direction of the terminal, and is crimped to the conductor exposed at a terminal of the electrical wire. The sheath crimping portion is provided closer to the rear than the conductor crimping portion in the longitudinal direction of the terminal, and is crimped to an insulation-coated portion of the electrical wire.
The conductor crimping portion is formed to have a substantially U-letter shaped cross section. The conductor crimping portion has a bottom plate, and a pair of conductor crimping pieces that are extended upward from both left and right side edges of the bottom plate and that crimp the conductor of the electrical wire arranged on an inner surface of the bottom plate so as to wrap it. The sheath crimping portion is formed to have a substantially U-letter shaped cross section. The sheath crimping portion has a bottom plate, and a pair of sheath crimping pieces that are extended upward from the both left and right side edges of the bottom plate and that crimp the electrical wire (insulation-coated portion) arranged on the inner surface of the bottom plate so as to wrap it. In an inner surface of the conductor crimping portion, provided is a plurality of concave groove-shaped serrations that extend in a direction perpendicular to a direction where the conductor of the electrical wire extends (terminal longitudinal direction).
FIG. 1(a) shows an expanded shape of a conductor crimping portion of a crimp terminal of a conventional example. A conductor crimping portion 213 of a crimp terminal 200 is formed of a bottom plate 215, and a pair of conductor crimping pieces 213a and 213a that are extended upward from both left and right side edges of the bottom plate 215 and that crimp a conductor of an electrical wire arranged on an inner surface of the bottom plate 215 so as to wrap it. Although FIG. 1(a) shows the expanded shape of the conductor crimping portion, actually, the conductor crimping portion 213 is bent to have a substantially U-letter shaped cross section in an uncrimped state. In an inner surface of the conductor crimping portion 213, provided is a plurality of concave groove-shaped serrations 220 that extend in a direction perpendicular to a direction where the conductor of the electrical wire extends.
FIG. 1(b) is an arrow cross-sectional view taken along a line B-B of FIG. 1(a). A cross-sectional shape of the concave groove-shaped serration 220 is usually a rectangle or an inverted trapezoid. In the present description, an angle θ between an extension surface of an inner bottom surface and an inner side surface of the serration 220 is called a serration angle. This serration angle θ is generally set in a range of 45 to 90 degrees.
In order to pressure-bond the conductor crimping portion 213 of the crimp terminal 200 to the conductor (illustration is omitted) of a terminal of the electrical wire, the crimp terminal 200 is placed on a placement surface (top surface) of a lower mold (an anvil, illustration is omitted), and the conductor of the electrical wire is inserted between the pair of conductor crimping pieces 213a and 213a of the conductor crimping portion 213 to be placed on the top surface of the bottom plate 215. Then, an upper mold (clamper) is then lowered relatively to the lower mold, and thereby tip sides of the conductor crimping pieces 213a are gradually tilted inside the crimp terminal 200 in a guide inclined surface of the upper mold. When the upper mold (clamper) is further lowered relatively to the lower mold, the tips of the conductor crimping pieces 213a and 213a are rounded so as to be folded to a conductor side in a curved surface continuous to a central chevron portion from the guide inclined surface of the upper mold, and bite into the conductor of the electrical wire while rubbing against each other. Thereby, the conductor crimping pieces 213a and 213a are crimped so as to wrap the conductor therein. By the above operation, the conductor crimping portion 213 of the crimp terminal 200 can be connected to the conductor of the electrical wire by crimping. In this crimping, the conductor of the electrical wire gets into the serrations 220 of the inner surface of the conductor crimping portion 213 while causing a plastic deformation by a pressure force. Thereby, electrical and mechanical joining of the terminal 200 and the electrical wire is enhanced.
By the way, when a shape of the concave serration 220, particularly the serration angle θ significantly decreases (herein, change of this serration angle is also referred to as “angle deformation”) by a pressure force at the time of crimping, a stress that is transmitted to an element wire of the conductor is reduced, thereby a serration function is not sufficiently exerted, and/or a relative sliding distance between the terminal and the conductor decreases, thereby an adhesion amount (a coupling amount of metal at a molecular or an atomic level) enough to sufficiently secure crimping performance can not be obtained. As a result of it, there is a problem of leading to deterioration of the crimping performance.
For example, as shown in FIG. 2(a), in a case of the conventional concave groove-shaped serrations 220, it has been confirmed that the serration angle significantly decreases as a compression rate becomes larger. In addition, although as shown in FIG. 2(b), a stress applied to the conductor increases as the compression rate becomes larger, it has been confirmed that an increase rate of the stress is considerably reduced in a case where angle deformation occurs as compared with a case where it does not occur.
Accordingly, in order to improve the crimping performance, it is important to make higher the stress working on the conductor and to increase an adhesion amount between the terminal and the conductor by crimping. In order to make the stress of the conductor higher and to increase the adhesion amount, it is necessary to sufficiently fulfill a serration function by suppressing the angle deformation of the serrations, and to increase a relative sliding distance between the terminal and the conductor.